1. Field of the Invention
This invention generally relates to a semiconductor device, and, in particular, to an electrically trimmable semiconductor device including at least one adjustable element, such as an adjustable capacitor or a variable resistor. More specifically, the present invention relates to a semiconductor device suitable for use as a clock I.C. or power supply I.C.
2. Description of the Prior Art
FIG. 1 schematically shows a prior art oscillating circuit for use in a typical clock I.C. As shown, an inverter 2 and a resistor 4 are provided in an I.C. as connected in parallel. Outside of the I.C. is provided a circuit including a quartz oscillator 6, a trimmer capacitor 8 and a capacitor 10 having a fixed capacitance, which is connected to the parallely connected inverter 2 and resistor 4 via a pair of terminals 28 and 29. In such an I.C. having an oscillating circuit incorporated therein, it is necessary to adjust the oscillating frequency one by one so as to obtain an accurate frequency. Such adjustment is typically carried out by operating the trimmer capacitor 8 provided outside of the body of I.C., for example, using a screw driver until the oscillating frequency reaches a desired value.
FIG. 2 shows a prior art constant power supply I.C., in which there is provided a bipolar transistor 12 which has its collector connected to an input terminal 13 and its emitter connected to an output terminal 15. The base of the bipolar transistor 12 is connected to an output terminal of a comparator 14 which has its non-inverting input terminal connected from the output terminal 15 through a resistor 16 and also from ground through a Zener diode 17. The comparator 14 has its inverting input terminal connected to a tap of a variable resistor 18 which is provided outside of the I.C. 19 and the variable resistor 18 has its one end connected to the output terminal 15 through a resistor and its other end connected to ground through another resistor. It is to be noted that the region 19 circumscribed by the one-dotted line corresponds to the interior of the I.C. In this constant power supply I.C., in order to obtain an accurate output voltage, the variable resistor 18 provided outside of the I.C. 19 is adjusted.
As described above, in the case of an I.C. requiring adjustments in capacitances and/or resistances, it is typical to provide an adjustable element, such as a trimmable capacitor or variable resistor, outside of the I.C. For this reason, the cost tends to be pushed up because of the necessity to provide an adjustable element outside of the I.C. Besides, the adjustment of such a trimmer capacitor or variable resistor must be carried out manually and mechanically by an operator for each I.C., which also tends to push up the cost. It is true that the adjustment can be carried out automatically using a laser trimming technology; however, a laser trimming apparatus is quite expensive and adjustment cannot be carried out after assembling, so that adjustment can be carried out only for a single I.C. and adjustment cannot be carried out by the user if an additional element is connected to the I.C.